There is a great need for olfactory or vapor-selective detectors (i.e., “artificial noses”) in a wide variety of applications. For example, there is a need for artificial noses that can detect low levels of odorants and/or where odorants may be harmful to humans, animals or plants. Artificial noses that can detect many different chemicals are desirable for personal dosimeters in order to detect the type and amount of odorants exposed to a human, the presence of chemical poisons or toxins, the spoilage in foods, the presence of flavorings, or the presence of vapor emitting items, such as plant materials, fruits and vegetables, e.g., at customs portals.
Conventional artificial noses have severe limitations and disadvantages and are not considered generally useful for such purposes. Limitations and disadvantages of conventional artificial noses include their need for extensive signal transduction hardware, and their inability to selectively target metal-coordinating vapors and toxins. In addition, artificial noses which incorporate mass sensitive signal transduction or polar polymers as sensor elements are susceptible to interference by water vapor. This limitation is significant in that it can cause variable response of the detector with changes ambient humidity. See F. L. Dickert, O. Hayden, Zenkel, M. E. Anal. Chem. 71, 1338 (1999).
Initial work in the field of artificial noses was conducted by Wilkens and Hatman in 1964, though the bulk of research done in this area has been carried out since the early 1980's. See, e.g., W. F. Wilkens, A. D. Hatman. Ann. NY Acad. Sci., 116, 608 (1964); K. Pursaud, G. H. Dodd. Nature, 299, 352-355 (1982); and J. W. Gardner, P. N. Bartlett. Sensors and Actuators B, 18-19, 211-220 (1994).
Vapor-selective detectors or “artificial noses” are typically based upon the production of an interpretable signal or display upon exposure to a vapor emitting substance or odorant (hereinafter sometimes referred to as an “analyte”). More specifically, typical artificial noses are based upon selective chemical binding or an interface between a detecting compound of the artificial nose and an analyte or odorant, and then transforming that chemical binding into a signal or display, i.e., signal transduction.
Polymer arrays having a single dye have been used for artificial noses. That is, a series of chemically-diverse polymers or polymer blends are chosen so that their composite response distinguishes a given odorant or analyte from others. Examples of polymer array vapor detectors, including conductive polymer and conductive polymer/carbon black composites, are discussed in: M. S. Freund, N. S. Lewis, Proc. Natl. Acad. Sci. USA 92, 2652-2656 (1995); B. J. Doleman, R. D. Sanner, E. J. Severin, R. H. Grubbs, N. S. Lewis, Anal. Chem. 70, 2560-2564 (1998); T. A. Dickinson, J. White, J. S. Kauer, D. R. Walt, Nature 382, 697-700 (1996)(polymer array with optical detection); A. E. Hoyt, A. J. Ricco, H. C. Yang, R. M. Crooks, J. Am. Chem. Soc. 117, 8672 (1995); and J. W. Grate, M. H. Abraham, Sensors and Actuators B 3, 85-111 (1991).
Other interface materials include functionalized self-assembled monolayers (SAM), metal oxides, and dendrimers. Signal transduction is commonly achieved with mass sensitive piezoelectric substrates, surface acoustic wave (SAW) transducers, or conductive materials. Optical transducers (based on absorbance or luminescence) have also been examined. Examples of metal oxide, SAM, and dendrimer-based detectors are discussed in J. W. Gardner, H. V. Shurmer, P. Corcoran, Sensors and Actuators B 4, 117-121 (1991); J. W. Gardner, H. V. Shurmer, T. T. Tan, Sensors and Actuators B 6, 71-75 (1992); and R. M. Crooks, A. J. Ricco, Acc. Chem. Res. 31, 219-227 (1998). These devices also use a single dye.
Techniques have also been developed using a metalloporphyrin for optical detection of a specific, single gas such as oxygen or ammonia, and for vapor detection by chemically interactive layers on quartz crystal microbalances. See A. E. Baron, J. D. S. Danielson, M. Gouterman, J. R. Wan, J. B. Callis, Rev. Sci. Instrum. 64, 3394-3402 (1993); J. Kavandi, et al., Rev. Sci. Instrum. 61, 3340-3347 (1990); W. Lee, et al., J. Mater. Chem. 3, 1031-1035 (1993); A. A. Vaughan, M. G. Baron, R. Narayanaswamy, Anal Comm. 33, 393-396 (1996); J. A. J. Brunink, et al., Anal. Chim. Acta 325, 53-64 (1996); C. Di Natale, et al., Sensors and Actuators B 44, 521-526 (1997); and C. DiNatale, et al., Mat. Sci. Eng. C 5, 209-215 (1998). However, these techniques either require extensive signal transduction hardware, or, as noted above, are limited to the detection of a specific, single gas. They are also subject to water vapor interference problems, as discussed previously.
While typical systems to date have demonstrated some success in chemical vapor detection and differentiation, these systems have focused on the detection of non-metal binding or non-metal ligating solvent vapors, such as arenes, halocarbons and ketones. Detection of metal-ligating vapors (such as amines, thiols, and phosphines) has been much less explored. Further, while some single porphyrin based sensors have been used for detection of a single strong acid, there is a need for sensor devices that will detect a wide variety of vapors.
To summarize, there are a number of limitations and drawbacks to typical artificial noses and single porphyrin based sensors. As noted above typical artificial noses are not designed for metal binding and metal ligating vapors, such as amines, thiols, and phosphines. Further, typical artificial noses require extensive signal transduction hardware, and are subject to interference from water vapor. As noted above, single porphyrin based sensors have been used for detection of a single strong acid, but cannot detect a wide variety of vapors. Thus, there is a need for new artificial noses and methods that overcome these and other limitations of prior artificial noses and single porphyrin based sensors and methods.